The present invention relates to a new type of process for the preparation of ether carboxylic acids with low residual alcohol content.
Ether carboxylic acids, i.e. organic carboxylic acids which, in addition to the carboxyl function, carry one or more ether bridges, or alkali metal or amine salts thereof, are known as mild detergents with high lime soap dispersibility. They are used both in detergent and cosmetic formulations, and also in industrial applications (e.g. metal working fluids, cooling lubricants). According to the prior art, these products are prepared either by alkylation of alcohol or fatty alcohol ethoxylates or propoxylates with chloroacetic acid derivatives (Williamson ether synthesis) or from the same starting materials by oxidation with various reagents (atmospheric oxygen, hypochlorite, chlorite) with catalysis with various catalysts. The disadvantage of the Williamson synthesis is the incomplete conversion of the parent ethoxylate to the ether carboxylic acid or salt thereof. Despite excesses of chloroacetic acid derivative, the conversions are often only between 70 and 85%. Residual amounts of ethoxylate or of the fatty alcohol on which the ethoxylate is based remain in the end-product since the former reacts more slowly with chloroacetic acid or the sodium salt of chloroacetic acid than an ethoxylated alcohol. This is particularly unfavorable when alcohols having low degrees of ethoxylation are used as base material. These ethoxylates can comprise between 5 and 30% of residual fatty alcohol. Since the fatty alcohol has lower reactivity in the Williamson synthesis than an ethoxylated fatty alcohol, this likewise leads to a high residual fatty alcohol content in the ether carboxylic acid and also to poorer conversions to the ether carboxylic acid. For this reason, using ethoxylates of lower fatty alcohol having chain lengths of C.sub.5 -C.sub.12 in the process often leads to odor problems as a result of the residual alcohol content since these fatty alcohols are odor-intensive.